Soil Types – Understanding Your Ground Conditions
The Problem
Soil isn’t just dirt — it’s a complex and variable material that can either support an excavation or cause it to collapse without warning. Many excavation-related injuries and fatalities happen because soil conditions are underestimated. Just as you wouldn’t build a house without understanding its foundation, you shouldn’t work in a trench without knowing the soil type. Today, we’ll cover the importance of soil classification and how it relates directly to safety on site.
Identify the Hazards
- Soil Failure: Trench walls can collapse suddenly if the wrong protective system is used for the soil type.
- Changing Conditions: Soil stability can be affected by rain, vibrations, or water seepage—sometimes within just a few hours.
- Worker Exposure: Being in or near an unsupported or unstable excavation places workers at serious risk of entrapment or injury.
Safety Practices and Preventative Measures
Understand the Types of Soil
Soils are classified by stability:
- Stable Rock: Solid and unbroken. Rare and often weakened by excavation techniques.
- Type A (Most Stable): High clay content, cohesive, and hard to break. Examples include clay, silty clay, and sandy clay. Cannot be Type A if water, fissures, or prior disturbance are present.
- Type B: Softer than Type A. May include previously disturbed soils and angular gravel.
- Type C (Least Stable): Loose materials such as sand, gravel, or soils with water present.
Competent Person’s Role
Only a competent person can classify soil. Their responsibilities include:
- Testing each layer or area of soil.
- Selecting the correct protective system (e.g., sloping, benching, shoring, or shielding).
- Monitoring for changing conditions such as water ingress or vibration.
- Making final decisions on whether work can proceed safely.
Adjust for Multiple Soil Types
- Sites often contain more than one soil type at different depths or areas.
- Each location must be individually tested and classified.
- Protective measures must match the least stable soil type present.
Stay Alert for Changing Conditions
- Rain, heavy machinery, or water seepage can instantly destabilize soil.
- If you see any signs of change, report it to the competent person immediately.
Real-Life Case or Scenario
On a trenching job, soil was initially classified as Type B. After unexpected rainfall, water seeped in, quickly changing conditions to Type C. Workers continued without reporting the change. A collapse occurred, burying one team member up to the waist. Quick thinking and a rescue team prevented a tragedy, but this incident could have been easily avoided if the soil had been reassessed after the rain.
Employee Responsibilities
Employer Responsibilities
- Appoint a competent person to classify and monitor soil conditions.
- Provide the appropriate protective systems for each trench (e.g., sloping, shoring, shielding).
- Train all workers in excavation safety and soil hazard awareness.
Discussion & Questions
- What types of soil do we usually encounter on our sites?
- How do weather events like heavy rain affect trench safety?
- Who is the competent person on this site, and how can we contact them?
- What steps should we take if we notice water seepage or soil shifting in a trench?
Encourage team members to share experiences and observations.
Commitment/Action Plan
Starting today, let’s commit to constantly monitoring soil conditions. If you notice any change in soil stability, don’t ignore it — report it to the competent person immediately. And remember: never enter an unstable or unsupported trench, no matter how quick the job seems.
Wrap-Up
Soil conditions can change in an instant—and understanding them is key to keeping everyone safe. By staying informed, following the competent person’s guidance, and reporting changes early, we can prevent trench collapses and protect our team. Thanks for staying alert and making safety a priority.
Standards Overview
Under Canadian occupational health and safety legislation and excavation safety guidelines:
- A competent person must assess soil conditions and determine the appropriate trench protection measures.
- Protective systems such as sloping, benching, shoring, or shielding must be used based on soil stability and classification.
- Soil conditions must be reassessed whenever site conditions change, such as after rain, water seepage, or nearby heavy equipment operation.
- Employers are responsible for ensuring workers are properly trained and that protective systems are installed, maintained, and inspected regularly.
Disclaimer
“The information provided in this toolbox talk is intended for informational and educational purposes only. It is not a substitute for professional legal, safety, or regulatory advice. The content reflects general best practices and industry standards but may not be applicable to all workplace environments or jurisdictions.
It is the responsibility of employers, supervisors, and workers to ensure compliance with applicable federal, provincial, and territorial laws, regulations, and standards, including but not limited to those set by the Canadian Centre for Occupational Health and Safety (CCOHS) and relevant provincial occupational health and safety authorities. Site App Pro, its affiliates, agents, or representatives—as well as the authors, presenters, and distributors of this toolbox talk—assume no liability for the use or application of the information provided.
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